The present disclosure relates to an apparatus and method for reading out an optical chip.
Optical structures such as ring resonators can be employed as sensors on an optical chip to detect one or more measurement parameters such as pressure, refractive index, presence of biomolecules, etcetera. These sensors can be part of an integrated optical circuit forming the optical chip. Typically, the optical circuit is externally addressable via an optical input and/or output. The sensor response can e.g. be measured by coupling source light into the optical input of the chip and collecting light from the optical output. While traversing the optical circuit, a property of the source light, e.g. intensity, can be modulated by interaction with the optical sensor, which interaction can be dependent on a measurement parameter. The measurement light collected from the optical output can be analysed and translated to yield an absolute or relative value of the parameter. Accordingly, the optical chip can be read out by coupling light into and out of the optical chip.
The coupling of source light into the chip as well as read-out and analysis of the measurement light received back is typically performed by an apparatus, also referred to as an analyser, that is specifically adapted to read out the chip, e.g. determine the measurement parameters of the chip. In case of employment as biosensors, e.g. as point-of-care diagnostic tests, a robust and cost effective coupling between the analyser and the sensor is desired that can be established in minimal time, e.g. seconds. Moreover, since these are typically disposable sensors, the coupling should preferably not add to the cost of the sensor too much.
One method to couple light into and out of an optical chip comprises the establishment of a permanent physical connection of optical fibres to the optical input and output ports of the chip, e.g. by adhesion or standard fibre connectors. However, for disposable sensor chips, such a permanent connection is too expensive because of labour and material costs. Furthermore, the connection may be fragile, e.g. the connected fibres may break. Accordingly, it is desired to avoid physical connections to and from the optical ports of the chip.
Another method to couple light into and out of an optical chip comprises illumination of one part of the chip with a broad beam and receiving light back from different location on the chip using a pixel array (camera). This method has the advantage that no physical connection to the optical ports of the chip is required. However, typically the optical chip accepts only a limited number of modes or even a single mode. Therefore, most of the broad light beam cannot enter the input port, and is lost. Furthermore, since most of the pixels are not used, pixel array is inefficient in collecting the light. Furthermore, the pixel array can be relatively expensive. Accordingly it is desired to provide a single in/out combined optical connection to efficiently irradiate and collect the light to and from the optical chip.
Yet another method to couple light into and out of an optical chip comprises bringing an array of input and output fibres close to the chip surface and holding them there during the sensor measurement. This method provides a cost benefit because it does not require physical connection to the optical ports of the chip. Furthermore this method can make relatively efficient use of the light because the fibre inputs and output can be targeted to specifically couple light to and from the optical ports. However, it can be difficult to establish an alignment between the optical fibres and optical ports of the chip, and the system may easily be damaged while inserting a new disposable chip.
For example, U.S. Pat. No. 5,926,594 describes a system for aligning and attaching optical fibers to optical waveguides in an integrated optic chip. Optical couplings to the waveguide legs include an input optical fibre positioned adjacent waveguide input leg, and a pair of output optical fibres respectively positioned adjacent the waveguide output legs. Light outputted from output optical fibres is directed respectively to different detectors, i.e. each fibre corresponds to different detection channel. Unfortunately, alignment of the system is rather complex involving a service robot, further alignment robots, an alignment plate, precision alignment pins, pre-alignment pins, and a goniometer.
For example, U.S. Pat. No. 7,378,861 B1 describes, wafer designs, testing systems and techniques for wafer-level optical testing by coupling probe light to/from the top of the wafer. A wafer level test system uses an optical probe to search for and aligning with an optical alignment loop. The test system uses a located alignment loop as a reference point to locate other devices on the wafer. A fine yaw optimization mechanism based on a yaw adjustment in the optical probe positioner and an alignment loop on the wafer may be implemented and operated in combination to address the alignment issue of a fibre array. However, the described alignment strategy may require dedicated structures on the wafer as well as a dedicated fibre probe which is not cost effective. Furthermore, the alignment is time consuming and requires sensitive actuators to coordinate the alignment of the plurality of the optical ports simultaneously.
Accordingly, a desire remains for an apparatus and method for reading out an optical chip that obviates one or more of the above discussed disadvantages while maintaining the advantages. In particular, it is desired to establish an efficient, robust, and cost effective optical coupling between the apparatus and optical chip in minimal time.